Carbonation curing method to produce wet-cast slag-based concrete products

ABSTRACT

The present description relates to methods of producing a wet-cast slag-based concrete product particularly where the wet-cast slag-based concrete product is cast, pre-conditioned and cured with carbon dioxide inside a mould and/or inside a mould placed in a curing chamber. The wet-cast slag-based concrete product is optionally reinforced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNumber PCT/CA2020/050467 filed on Apr. 9, 2020, which claimed priorityto U.S. Provisional Patent Application No. 62/832,966 filed on Apr. 12,2019, the contents of both of which said applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present description relates to methods of producing a wet-castslag-based concrete product particularly where the wet-cast slag-basedconcrete product is cast, pre-conditioned and cured with carbon dioxideinside a mould and/or inside a mould placed in a curing chamber. Thewet-cast slag-based concrete product is optionally reinforced.

BACKGROUND OF THE INVENTION

Metallurgical slag is an abundant waste material that is usuallylandfilled. Metallurgical slag may act as a binder material underappropriate conditions. Finding new uses for metallurgical slag,including steel slag, are required.

SUMMARY

Development of concrete products, that are optionally reinforced, andmade from a metallurgical slag as the main binder and carbon dioxidewith the wet-cast method is explained herein.

In accordance with one aspect there is provided a method of producing awet-cast slag-based concrete product comprising steps of: providing acomposition for a non-zero-slump concrete, the composition comprising aslag based binder, an aggregate and water; mixing the slag based binder,the aggregate and the water to produce the workable non-zero-slumpconcrete comprising a first water to binder ratio by weight of greaterthan 0.2; casting/placing the non-zero-slump concrete bytransferring/consolidating the non-zero-slump concrete into an air-tightmould comprising at least one gas pipe/lance; pre-conditioning thenon-zero-slump concrete within the mould with at least one of i) airflow/pressurized air from the at least one gas lance, ii) heaters andiii) heating element wires embedded in concrete, to produce aconditioned slag-based intermediate comprising a second water to binderratio by weight that is less than the first water to binder ratio byweight; sealing the air-tight mould; curing the conditioned slag-basedintermediate with a gas containing carbon dioxide from the at least onegas lance to activate the conditioned slag-based intermediate andproduce the wet-cast slag-based concrete product, and demouldingwet-cast slag-based concrete product.

In accordance with another aspect there is provided the method describedherein, wherein the casting of the non-zero-slump concrete is free ofpressing/compaction.

In accordance with yet another aspect there is provided the methoddescribed herein, wherein after curing, filling a hollow space withinthe at least one gas lance with cement grout, steel fiber reinforcedcement mortar and cement paste.

In accordance with still yet another aspect there is provided the methoddescribed herein, the gas lance may be inserted after casting thenon-zero-slump concrete.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag-based binder is a slag—free of ormixed with at least one other binder selected from the group furtherconsisting of fly ash, calcinated shale, silica fume, zeolite, GGBF(Ground Granulated Blast Furnace) slag, limestone powder, hydrauliccements and non-hydraulic cements.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag is selected from the group consistingof a steel slag, a stainless steel slag, a basic oxygen convertersludge, blast furnace sludge, a by-product of zinc, iron, copperindustries and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, further comprising a reinforcing step of placing areinforcing material into the air-tight mould before the casting step.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the reinforcing material is carbon steel,stainless steel and/or fiber reinforced polymer (FRP) reinforcementbars.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein a cumulative calcium silicate content of theslag is at least 20 weight %.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the pre-conditioning increases porosity of atleast 1% of volume of the wet-cast slag-based concrete.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a slump valuein a range of 5 mm to 250 mm.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a compactionfactor test for the fresh concrete must find a value in the range of 0.7to 1.0.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the steel slag is selected from the groupconsisting of reducing steel slag, oxidizing steel slag, converter steelslag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag(BOF slag), ladle slag, fast-cooled steel slag and slow-cooled steelslag and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete is furtherprocessed to a product selected from the group consisting of precast,reinforced and non-reinforced concrete pipes, box culverts, drainageproducts, paving slabs, floor slabs, traffic barriers, walls manholes,retaining wall, pavers, tiles, and shingles.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete comprises ofa slag content of at least 5% by weight.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one accelerator, retarder, viscosity modifying agent, airentertainer, foaming agent, ASR (alkali silica reaction) inhibitor,anti-wash-out, corrosion inhibitor, shrinkage reducer, concrete crackreducer, plasticizer, super plasticizer, sealer, paint, coating, waterreducer, water repellant, efflorescence control, polymer powder, polymerlatex and workability retainer.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one cellulose fiber, glass fiber, micro synthetic fiber,natural fiber, polypropylene (PP) fiber, polyvinyl alcohol (PVA) fiberand steel fiber.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the CO₂ curing is free of additional externalsources of heat/energy.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the demoulded conditioned slag-basedintermediate is cured in a chamber/enclosed space/vessel/room with a gascontaining a concentration of CO₂ of at least 5% by volume.

In accordance with still yet another aspect there is provided a methodof producing a wet-cast slag-based concrete product comprising steps of:providing a composition for a non-zero-slump concrete, the compositioncomprising a slag based binder, an aggregate and water; mixing the slagbased binder, the aggregate and the water to produce the workablenon-zero-slump concrete comprising a first water to binder ratio byweight of greater than 0.2; casting/placing the non-zero-slump concreteby transferring/consolidating the non-zero-slump concrete into anair-tight mould, the mould comprising a mould wall and a plurality ofinlets in the mould wall, wherein the plurality of inlets are optionallyclosed to retain the slurry non-zero-slump concrete; pre-conditioningthe non-zero-slump concrete within the mould with at least one of i) anair flow/pressurized air through the plurality of inlets in the mouldwall, ii) heaters and iii) heating element wires embedded in concrete,to produce a conditioned slag-based intermediate comprising a secondwater to binder ratio by weight that is less than the first water tobinder ratio by weight; sealing the mould; curing the conditionedslag-based intermediate with a gas containing carbon dioxide via theplurality of inlets in the mould wall connected to a source of the gasto activate the conditioned slag-based intermediate and produce thewet-cast slag-based concrete product, and demoulding wet-cast slag-basedconcrete product.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the casting of the non-zero-slump concrete isfree of pressing/compaction.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein at least one perforated tube is optionallyinserted through one of the inlets.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the at least one perforated tube is insertedinto the air-tight mould interior and traverses either fully orpartially to an opposite mould wall.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag-based binder is a slag—free of ormixed with at least one other binder selected from the group furtherconsisting of fly ash, calcinated shale, silica fume, zeolite, GGBF(Ground Granulated Blast Furnace) slag, limestone powder, hydrauliccements and non-hydraulic cements.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag is selected from the group consistingof a steel slag, a stainless steel slag, a basic oxygen convertersludge, blast furnace sludge, a by-product of zinc, iron, copperindustries and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, further comprising a reinforcing step of placing areinforcing material into the air-tight mould before the casting step.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the reinforcing material is carbon steel,stainless steel and/or FRP reinforcement bars.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein a cumulative calcium silicate content of theslag is at least 20 weight %.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the pre-conditioning increases porosity of atleast 1% of volume of the wet-cast slag-based concrete.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a slump valuein a range of 5 mm to 250 mm.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a compactionfactor test for the fresh concrete must find a value in the range of 0.7to 1.0.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the steel slag is selected from the groupconsisting of reducing steel slag, oxidizing steel slag, converter steelslag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag(BOF slag), ladle slag, fast-cooled steel slag and slow-cooled steelslag and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete is furtherprocessed to a product selected from the group consisting of precast,reinforced and non-reinforced concrete pipes, box culverts, drainageproducts, paving slabs, floor slabs, traffic barriers, walls manholes,retaining wall, pavers, tiles, and shingles.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete comprises ofa slag content of at least 5% by weight.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one accelerator, retarder, viscosity modifying agent, airentertainer, foaming agent, ASR (alkali silicati reaction) inhibitor,anti-wash-out, corrosion inhibitor, shrinkage reducer, concrete crackreducer, plasticizer, super plasticizer, sealer, paint, coating, waterreducer, water repellant, efflorescence control, polymer powder, polymerlatex and workability retainer.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one cellulose fiber, glass fiber, micro synthetic fiber,natural fiber, PP fiber, PVA fiber and steel fiber.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the CO₂ curing is free of additional externalsources of heat/energy.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the demoulded conditioned slag-basedintermediate is cured in a chamber/enclosed space/vessel/room with a gascontaining a concentration of CO₂ of at least 5% by volume.

In accordance with still yet another aspect there is provided a methodof producing a wet-cast slag-based concrete product comprising steps of:providing a composition for a non-zero-slump concrete, the compositioncomprising a slag based binder, an aggregate and water; mixing the slagbased binder, the aggregate and the water to produce the workablenon-zero-slump concrete comprising a first water to binder ratio byweight of greater than 0.2; casting/placing the non-zero-slump concreteby transferring/consolidating the non-zero-slump concrete into a mould,the mould comprising a mould wall defining an open top surface and aplurality of inlets in the mould wall, wherein the plurality of inletsare optionally closed to retain the workable non-zero-slump concrete;pre-conditioning the non-zero-slump concrete within the mould with atleast one of i) an air flow/pressurized air through the plurality ofinlets, ii) heaters and iii) heating wire elements embedded in concreteto produce a conditioned slag-based intermediate comprising a secondslag to water ratio by weight that is less than the first slag to waterratio by weight; curing the conditioned slag-based intermediate with agas containing carbon dioxide in a chamber/enclosed space/vessel/roomvia the plurality of inlets in the mould wall and the open top surfaceto activate the conditioned slag-based intermediate and produce thewet-cast slag-based concrete product, and demoulding wet-cast slag-basedconcrete product.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the casting of the non-zero-slump concrete isfree of pressing/compaction.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag-based binder is a slag—free of ormixed with at least one other binder selected from the group furtherconsisting of fly ash, calcinated shale, silica fume, zeolite, GGBF(Ground Granulated Blast Furnace) slag, limestone powder, hydrauliccements and non-hydraulic cements.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the slag is selected from the group consistingof a steel slag, a stainless steel slag, a basic oxygen convertersludge, blast furnace sludge, a by-product of zinc, iron, copperindustries and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, further comprising a reinforcing step of placing areinforcing material into the mould before the casting step.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the reinforcing material is carbon steel,stainless steel and/or FRP reinforcement bars.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein a cumulative calcium silicate content of theslag is at least 20 weight %.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the pre-conditioning increases porosity of atleast 1% of volume of the wet-cast slag-based concrete.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a slump valuein a range of 5 mm to 250 mm.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete has a compactionfactor test for the fresh concrete must find a value in the range of 0.7to 1.0.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the steel slag is selected from the groupconsisting of reducing steel slag, oxidizing steel slag, converter steelslag, electrical arc furnace slag (EAF slag), basic oxygen furnace slag(BOF slag), ladle slag, fast-cooled steel slag and slow-cooled steelslag and combinations thereof.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete is furtherprocessed to a product selected from the group consisting of precast,reinforced and non-reinforced concrete pipes, box culverts, drainageproducts, paving slabs, floor slabs, traffic barriers, walls manholes,retaining wall, pavers, tiles, and shingles.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the wet-cast slag-based concrete comprises ofa slag content of at least 5% by weight.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one accelerator, retarder, viscosity modifying agent, airentertainer, foaming agent, ASR (alkali silicati reaction) inhibitor,anti-wash-out, corrosion inhibitor, shrinkage reducer, concrete crackreducer, plasticizer, super plasticizer, sealer, paint, coating, waterreducer, water repellant, efflorescence control, polymer powder, polymerlatex and workability retainer.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the non-zero-slump concrete further comprisesat least one cellulose fiber, glass fiber, micro synthetic fiber,natural fiber, PP fiber, PVA fiber and steel fiber.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the CO₂ curing is free of additional externalsources of heat/energy.

In accordance with still yet another aspect there is provided the methoddescribed herein, wherein the conditioned slag-based intermediate iscured in a chamber/enclosed space/vessel/room with a gas containing aconcentration of CO₂ of at least 5% by volume.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1. is a process block diagram illustrating a method of producing awet-cast slag-based concrete product with casting, preconditioning andCO₂ curing undertaken in a sealed mould with a gas pipe/lance accordingto one embodiment of described herein;

FIG. 2 is a schematic representation of a front view section of thecasting, pre-conditioning and CO₂ curing steps in a sealed mouldaccording to one embodiment described in FIG. 1 herein;

FIG. 3 is a schematic representation of a front view section of thecasting, pre-conditioning and CO₂ curing steps in a sealed mouldaccording to another embodiment described in FIG. 1 herein;

FIG. 4 is a process block diagram illustrating another method ofproducing a wet-cast slag-based concrete product with casting,preconditioning and CO₂ curing undertaken in a sealed mould with aplurality of holes in the mould for gas entry according to anotherembodiment of described herein;

FIG. 5 is a schematic representation of a front view section of thecasting, pre-conditioning and CO₂ curing steps in a sealed mouldaccording to one embodiment described herein in FIG. 4;

FIG. 6 is a schematic representation of a front view section of thecasting, pre-conditioning and CO₂ curing steps in a sealed mouldaccording to another embodiment described herein in FIG. 4;

FIG. 7 is a process block diagram illustrating a further method ofproducing a wet-cast slag-based concrete product with casting,preconditioning and CO₂ curing undertaken in an open topped, un-sealed,mould with a plurality of holes in side walls of the mould, that isplaced in a curing chamber or sealed enclosure according to anotherembodiment of described herein; and

FIG. 8 is a schematic representation of a front view section of thecasting, pre-conditioning and CO₂ curing steps in an un-sealed mouldwithin a curing chamber or other gas enclosure according to oneembodiment described herein in FIG. 7.

DETAILED DESCRIPTION

Traditionally, newly sintered Portland cement is used as the binder inconcrete production, and wet-cast cement-based precast concrete productsare commonly cured with heat and steam. The present innovation ofwet-cast slag-based concrete in contrast uses by-products ofmetallurgical plants and in a preferred embodiment—steelmaking factoriesas the main binder to replace Portland cement in production of concreteand precast products. In addition, carbon dioxide is used as anactivator to cure the concrete and is sequestered in the process. Inpreferred embodiment, no additional heat or steam are needed during theCO₂ curing process. The proposed wet-cast slag-based concrete products,that are optionally reinforced, may show equal or superior mechanicaland durability properties when compared to the traditional cement-basedprecast products, while their production would reduce greenhouse gasemissions to the atmosphere. The proposed innovation would also reduceconsumption of natural resources, both as conventional cement is notused in the slag-based concrete products and as a lower amounts ofaggregate content are needed in the slag-based concrete products.Finally, the production of wet-cast slag-based concrete products,optionally reinforced, according to the proposed innovation may increaseproduction rate at the precast concrete making facilities.

Materials

The main binder in the production of wet-cast slag-based concrete is aslag that in a preferred embodiment derives from steel or stainlesssteel production. Other by-product materials from zinc, iron, and copperproduction can also be considered as the slag.

Various slags can be collected from steel factories that practicedifferent methods of steel production. Among the types of slag that canbe incorporated as the main binder in production of wet-cast slag-basedconcrete described herein is: stainless steel slag, reducing steel slag,oxidizing steel slag, converter steel slag, electrical arc furnace slag(EAF slag), basic oxygen furnace slag (BOF slag), ladle slag,fast-cooled steel slag, slow-cooled steel slag, basic oxygen convertersludge, blast furnace sludge and combinations thereof.

The calcium oxide content by weight of slag in an preferred embodimentis more that 10%, preferably more than 15%, preferably more than 20%.The silica oxide content by weight in a preferred embodiment is morethan 6%, preferably more than 8%, preferably more than 12%. The totaliron oxide content of slag in a preferred embodiment is less than 40%,preferably less than 30%. Steel slag in a preferred embodiment has acumulative calcium silicate content of at least 20% and a free limeconcentration of less than 15%, and preferably less than 7% slag. Thebulk density of the slag in a preferred embodiment has a range of 1.0 to2.0 g/cm³ and an apparent density may vary from 2.0 to 6.0 g/cm³.

The slag may be ground to a smaller size (if required) before beingincorporated into the wet-cast slag-based concrete mix described herein.Grinding the slag can be performed with any mechanical machine such as aball mill, rod mill, autogenous mill, SAG mill, pebble mill, highpressure grinding rolls, VSI or tower mill. The grinding process can beexecuted either wet or dry. While a dry size reduction process ispreferred, if the wet process is chosen for grinding the slag, theground slag can be either dried completely or semi-dried after grinding.Passing the slag through a classifier(s) is an alternative option toobtain slag with a smaller particle/grain size. The classifiers used areknown in the art and include but are not limited to: screens;centrifuges and cyclones.

Ground or classified slags in a preferred embodiment pass through a mesh#10 (2000 microns), preferably a mesh #50 (297 microns), preferably amesh #200 (74 microns), preferably a mesh #400 (37 microns) each ofwhich can be used alone or in combination with at least one otherbinder. Sieves may be utilized to screen slags either after or beforegrinding. Thus, one or combination of grinding and screening methods canbe executed in order to obtain slag with a proper particle sizedistribution.

The slag may be pulverized and/or screened to a Blaine fineness of atleast 50 m²/kg and preferably, 150 m²/kg, and preferably at least 200m²/kg. In a preferred embodiment the slag in slag-based wet concrete,fifty percent of slag is smaller than 200 microns (D50=200 μm),preferably smaller than 150 microns (D50=150 μm), preferably smallerthan 100 microns (D50=100 μm), preferably smaller than 50 microns(D50=50 μm), preferably smaller than 25 microns (D50=25 μm), preferablysmaller than 10 microns (D50=10 μm).

The free lime content of the slag may be reduced with any standard knownmethod in the prior art before it is incorporated into the mix.Alternatively, the slag can first be aged to reduce its free calciumoxide (free lime) content and then incorporated into the mix. Slagcontent of wet-cast slag-based concrete should be no less than 5% of theweight of concrete, preferably no less than 20% of the weight of thewet-cast slag-based concrete or the non-zero-slump concrete composition.

The slag-based binders may further comprise: a slag alone (i.e. a slagthat is-free of another binder) or be a combination of slag with atleast one other binder, such as cementitious materials/pozzolanicmaterials. As an example, slag can be mixed with at least one otherbinder producing a slag-based binder further comprising: fly ash,calcinated shale, silica fume, zeolite, GGBF (Ground Granulated BlastFurnace) slag, limestone powder, hydraulic cements, non-hydrauliccements and combinations thereof.

Various types of aggregate—including natural or artificial normal weightand lightweight aggregates—can be incorporated into the slag-based wetconcrete product as filler in the production of wet-cast slag-basedconcrete product. Examples of potential lightweight aggregates includesnatural lightweight aggregate (e.g. pumice), expanded clay aggregate,expanded shale aggregate and expanded iron slag aggregate. Other usableaggregates include: crushed stone, manufactured sand, gravel, sand,recycled aggregate, granite, limestone, quartz, chalk powder, marblepowder, quartz sand and artificial aggregate. These aggregates areincorporated into the mix as fine and/or coarse aggregates. Aggregatecontent can be as high as 90% of the weight of the wet-cast slag-basedconcrete or the non-zero-slump concrete composition.

The proposed slag-based wet concrete is a workable concrete. Enoughwater should be added to the dry ingredient in order to produce a wetconcrete (in contrast with slump-zero concrete). The required watercontent depends on the grain size of the slag chosen as the main binderand on the moisture content of the aggregates and content of binder.Finer ground slags absorb more water, so a higher water content would berequired to produce wet concrete. Water-to binder ratio, in mass, can be0.9, preferably 0.8, preferably 0.7, preferably 0.6, preferably 0.5,preferably 0.4, preferably 0.3, or preferably 0.2. For example, for thebinder consisting of only slag with D50 of 25 microns, the water tobinder ratio of 0.4 can result in a workable wet concrete. It may be thecase that no additional water is required in the mix if the aggregatesare very wet.

Chemical admixtures, can be introduced into the mix if required.Chemical admixtures when introduced into the mix satisfy specificproperties. Possible chemical admixtures include but are not limited to:accelerators, retarders, viscosity modifying agents, air entertainers,foaming agents, ASR (alkali silica reaction) inhibitors, anti-wash-out,corrosion inhibitors, shrinkage reducers, crack reducers, plasticizers,super plasticizers, water reducers, water repellants, efflorescencecontrols and workability retainers.

Fibers can be added if required to the slag-based wet concrete. One orcombination of cellulous fiber, glass fiber, micro synthetic fibers,micro synthetic fibers, natural fibers, PP fibers, PVA fibers and steelfibers can be incorporated into the mix.

The “zero-slump concrete” is defined as a concrete of stiff or extremelydry consistency showing no measurable slump after removal of the slumpcone. A standard exemplary slump test is ASTM C143, for Hydraulic-CementConcrete. A non-zero-slump concrete is a concrete that is not stiff norextremely dry consistency showing a measurable slump after removal ofthe slump cone by a test such as ASTM C143. The slump values herein areassessed using the method described in the ASTM C143 standard.

The method of producing a wet-cast slag-based concrete can be adapted toproduce a variety of products including but not limited to precast,reinforced concrete pipes, box culverts, drainage products, pavingslabs, floor slabs, traffic barriers, walls, manholes, precastnon-reinforced concrete (plain) pavers, retaining walls, tiles andshingles. The products shall satisfy local and national standards andcodes.

Turning to the figures, FIGS. 1, 4 and 7 presented here illustrate threeembodiments of process flow diagrams of the method of producing awet-cast slag-based concrete product. The three-digit reference numeralsused in FIGS. 1, 4 and 7 include a single digit prefix 1XX, 2XX and 3XXrespectively. The two digit suffix of the reference numeral representsthe same feature in each of the FIGS. 1, 4 and 7. That is, referencenumerals 120, 220 and 320 for example, each represent the unit operationof casting in their respective process flow diagram, specifically FIGS.1, 4 and 7 respectively.

A) A Sealed Mould with Gas Pipes/Lances Passed Through Top Surface/Lidof the Mould

Referring to FIG. 1, a method 101 of producing a wet-cast slag-basedconcrete product 156 is outlined with steps including casting,pre-conditioning and CO₂ curing in a sealed air-tight mould with atleast one gas pipe/lance.

(i) Wet-Cast Slag-Based Concrete 156 Production.

The method 101 of wet-cast slag-based concrete 156 begins by providing acomposition of a non-zero-slump concrete 116 and uniformly mixing 110all ingredients of a composition that include but are not limited to: aslag 111 and an optional at least one other binder 113 that when mixedprovides a slag-based binder 114 (i.e. slag alone or slag with at leastone other binder), an aggregate 115, chemical admixtures 117, fibers 119and water 105. The water-to-binder ratio of the wet-cast slag-basedconcrete 156 used in this innovation should be higher than the watercontent of dry-cast or zero-slump concrete. In a preferred embodimentthe mixed non-zero-slump concrete 116 has a first water to binder ratioby weight of greater than 0.2, preferably 0.25, preferably 0.3,preferably 0.35, preferably 0.4, preferably 0.45, preferably 0.5,preferably 0.55, preferably 0.6 or preferably 0.65. The terms “water toslag-based binder ratio by weight” and “water to binder ratio by weight”are equivalents.

The non-zero-slump concrete 116 will preferably have a slump range of 5to 250 mm. The non-zero-slump concrete 116 is preferably workable for atleast 5 minutes. The mixing 110 should ensure that the non-zero-slumpconcrete 116 is free of signs of segregation or bleeding. The compactionfactor test for the non-zero-slump concrete 116 in a preferredembodiment is in a range of 0.7 to 1.0. The temperature ofnon-zero-slump concrete 116 before casting is preferably 0° C. to 30° C.The fresh non-zero-slump concrete 116 in a preferred embodiment has anair void content as measured by any conventional method (an exemplarystandardized test is ASTM C231 for Air Content of Freshly Mixed Concreteby the Pressure Method) should not exceed 15% of the volume of concrete.The compaction factor test is described in BS 1881-103:1993 and BS EN12350-4:2009 (BS EN 12350-4:2009, Testing fresh concrete Part 4: Degreeof compatibility). The non-zero-slump concrete 116 appropriately mixedis now ready for transfer to casting 120.

(ii) Reinforcement

In a preferred embodiment before casting the non-zero-slump concrete 116the mould is prepared and reinforcing material such as, carbon steel,stainless steel and/or FRP reinforcement bars are placed inside theair-tight mould, if required. The diameter of the bars may vary from 5mm to 60 mm with yield strength in the range of 100 MPa to 2100 MPa. Thereinforcements to be designed in accordance with codes and standards.

(iii) Casting 120, Placement

Punched hollow pipes/lances are placed in the air-tight mould. Theirgeometry can be circular or rectangular, with a cross-sectional arealess than 10,000 mm² per pipe, and wall thickness greater than 0.5 mm.The pipe/lance material can be carbon steel, stainless steel or alloysteel with carbon content of 0.05% to 1.4%, ensuring a yield strengthfor the pipe/lance between 100 MPa to 2100 MPa. Pipes/lances can bepunched with mechanical tools, manual apparatuses or any tool thatcreate holes via shearing. In an optional embodiment the pipes/lancesmay be made of a permeable screen/mesh material compatible for theirfunction. The maximum size of the holes should be 10 mm, preferably 5mm, or preferably 1 mm. Hole intervals, in both vertical and horizontaldirections, should not be more than 300 mm, preferably 200 mm,preferably 100 mm, preferably 50 mm. In another example, the punchedhollow pipes are made of aluminum or plastic. The pipe/lance will beused to transfer gas into the non-zero-slump concrete 116.

The freshly prepared non-zero-slump concrete 116 is transferred byappropriate means and cast in a prepared mould with any known methods inthe prior arts. The mould can be made of steel, iron, aluminum, plastic,FRP or other material. The mould should be airtight and is sealed usinga lid designed to cover and enclose the top of the mould in one of thepossible mould materials or in airtight fabrics. This lid is attached tothe body of the mould with hinges, clamps and/or bolts. A few preciselymachined holes are cut in the lid to allow punched hollow pipes/lancesto pass through the mould lid. In another example, the pipes/lances canbe inserted into the concrete/mould right after casting concrete. Thelid can be initially attached to the mould prior to the casting or inother examples it can be mounted on the mould after casting concrete.

The mould should be pre-lubricated prior to casting in order tofacilitate the demoulding process 130. The wet-cast concrete or theslag-based intermediate 126 is consolidated within the mould by internalor external vibrators for no more than 120 seconds. The wet-castconcrete or the slag-based intermediate 126 does not need to be pressedor compacted inside the mould. That is, the present method in apreferred embodiment is free of being pressed or compacted. The watercontent of a slag-based intermediate 126 must be reduced.

(iv) Pre-Conditioning 140

The process step of pre-conditioning 140 reduces the water content ofnon-zero-slump concrete 116 with the removal of water 142.Pre-conditioning may be conducted in at least one of two ways. In thefirst method, air flow 141 is introduced through the hollow pipes/lances(FIG. 2). In another example the air flow can be pressurized air. Thelid is not required to be closed in the preconditioning step. Thispreconditioning step continues with water vapour 142 leaving the moulduntil initial the water-to-binder content is reduced by up to 90%,preferably 80%, preferably 70%, preferably 60%, preferably 50%,preferably 40%, preferably 30%, preferably 20% or preferably 10%. Thesecond method uses heating element wires 143 that in a preferredembodiment are embedded in the concrete. These wires are placed in themould before casting the concrete (FIG. 3). They may also be placed on asteel frame across the height of the mould at an interval of 300 mm. Theheating wires and frame are left inside the concrete when it is cast andafter concrete is cured. An electric current can then be passed throughthe frame and wires. Alternatively, heaters may be used, such as floorheating mats or drum heaters that can be installed so as to cover theexterior surfaces of the mould. The elements heat up the mould walls andeventually increase the evaporation process to reduce the moisturecontent of the concrete. The two methods may furthermore be combined toinclude both air 141 drying and heating 143.

The preconditioning 140 step continues until initial water-to-bindercontent is reduced by up to 90%, preferably 80%, preferably 70%,preferably 60%, preferably 50%, preferably 40%, preferably 30%,preferably 20% and preferably 10% or preferably 2% and the slag-basedintermediate 126 is produced.

The increase of porosity defined in terms of concrete volume created byeither of the above pre-conditioning methods in concrete is 70%,preferably 60%, preferably 50%, preferably 40%, preferably 30%,preferably 20%, preferably 10% or preferably 5% or preferably 1% ofconcrete volume. After either method, the mould is sealed, the lidclosed and the mould is inspected for airtightness, with carefulattention to the openings that allow the hollow gas pipes/lances toprotrude.

At the end of the pre-conditioning 140 process, the remaining water inthe concrete should not fall below 5% of the initial water content bymass and a conditioned slag-based intermediate 146 is formed, having asecond water to binder ratio by weight that is less than the first waterto binder ratio of the non-zero-slump concrete 116. The mould is sealedair-tight after completion of the pre-conditioning step 140.

(v) CO₂ Activation\Curing 150

The conditioned slag-based intermediate 146 is contacted with carbondioxide, CO₂ or gas mixture thereof. The carbon dioxide 151 gas isintroduced to cure the conditioned slag-based intermediate 146 at 5%,preferably 10%, preferably 20%, preferably 30%, preferably 40%,preferably 50%, preferably 60%, preferably 70%, preferably 80%,preferably 90%, or preferably 99.5% purity—into the conditionedslag-based intermediate 146 at ambient temperature through the punchedhollow pipes/lances. The gauge pressure of the chamber/enclosedspace/vessel/room will gradually increase to a range of 0.1 psi to 100psi. Although not illustrated it is understood that some gases mayescape the CO₂ activation\curing step.

With this embodiment of the invention, the sealed mould also operates asa curing chamber. The mould is kept pressurized with carbon dioxide forno less than 10 minutes, though the CO₂ curing process can continue forup to 48 hours. The inner mould temperature will increase by at least 1°C. as a result of an exothermic, accelerated curing reaction—the “CO₂activation process”. At the end of the activation process, the remainingCO₂, if any, is vented out and the lid opened. The pipes/lances can beleft inside the concrete or removed from it. It is understood that ahollow space remains within the at least one gas lance, that can befilled with a cement grout, a steel fiber reinforced cement mortar, acement paste or a polymer concrete. This filling of the gas lance occursafter CO₂ curing or demoulding.

(vi) Demoulding 130

Demoulding occurs soon or immediately after the CO₂ activation process.The excess lengths of punched hollow pipes/lances (if they are leftinside the concrete) are cut off and the hollow pipes or created spacesare filled 155 with a cement grout, a steel fiber reinforced cementmortar, a cement paste, a polymer concrete or combinations thereof. Thecement or polymer-based filling materials are cured for no less than 1hour.

Upon demoulding 130 a wet-cast slag-based concrete 156 is produced.

B) A Sealed Mould with Holes on the Side Walls of the Mould.

Referring to FIG. 4, a method 201 is outlined for producing a wet-castslag-based concrete product 256 with steps including casting,preconditioning and CO₂ curing in a sealed mould with a plurality ofholes in the mould for gas entry.

(i) Wet-Cast Slag-Based Concrete 256 Production.

The method 201 of wet-cast slag-based concrete 256 production begins inthe same way as that previously described for wet-cast slag-basedconcrete 156. A composition of a non-zero-slump concrete 216, isuniformly mixed 210, with the ingredients of a composition that includebut once again are not limited to: a slag 211 and an optional at leastone other binder 213 (providing a slag-based binder 214), an aggregate215, chemical admixtures 217, fibers 219 and water 205. All theproperties of the wet-cast slag-based concrete 256 are the same as thatpreviously described for wet-cast slag-based concrete 256.

The mixing 210 once again ensures that the non-zero-slump concrete 216is free of signs of segregation or bleeding.

(ii) Reinforcement

As described before in FIG. 1 with the wet-cast slag-based concrete 156,the wet-cast slag-based concrete 256, optionally includes an air-tightmould prepared with reinforcing material as previously described.

(iii) Casting 220, Placement

The mould for method 201 can once again be made of steel, iron,aluminum, plastic, or FRP. The mould is preferably air-tight andsealable using a lid designed with a top cover in a material previouslydescribed after transferring the non-zero-slump concrete 256. The lid ofthe air-tight mould is once again attached to the body of the mould witha combination of hinges, clamps and/or bolts. The embodiment of method201 does not require special openings for a gas pipe/lance of theprevious embodiment in the lid of the mould.

Two different types of air-tight moulds are presented for two differentconstruction methods the two embodiment of method 201. In the embodimentof the schematic illustration of FIG. 5, the mould has a plurality ofsmall holes in the side walls. The maximum diameter of these holesshould not exceed 10 mm. The interval between adjacent holes in bothvertical and horizontal directions should not be more than 300 mm. In asecond embodiment of method 201 shown in FIG. 6, the air-tight mould hasa plurality of fewer but larger holes in the side walls (maximuminterval of the larger holes is 500 mm, 400 mm, 300 mm, preferably 200mm, preferably 100 mm, preferably 50 mm) that include at least oneperforated tubes passing through the larger mould sidewall holes. Thediameter of the larger holes in the walls of the mould should fall inthe range of 10 mm to 200 mm. Holes are optionally closed to retain thefresh non-zero-slump concrete. The perforated tubes placed in the mouldwall are made of steel, FRP, stainless steel, plastic or aluminum. Theseperforate tubes optionally traverse the mould interior until reachingthe other side or until they end at some distance within the mould. Thecross section, interval and area of the tubes matches that of holes inthe side walls. The perforated tubes are permeable to gases and definemany orifices preferably having a maximum spacing between each orificeof 30 mm. The perforated tubes may be inserted into the air-tight mouldinterior so as to traverse either fully or partially to an oppositemould wall. The hollow space left within the perforated tubes and holesof the sidewall can be sealed by methods known to a person skilled inthe art.

The perforated tubes are placed in the walls of the mould may have awall thickness greater than 0.5 mm. The perforated tubes material can becarbon steel, stainless steel or alloy steel with carbon content of0.05% to 1.4%, and strength of 100 MPa to 2100 MPa. Perforated tubes canbe punched with mechanical tools, manual apparatuses or any tool thatcreate holes via shearing, or of a compatible permeable screen material.The maximum size of the holes should be 10 mm, preferably 5 mm, orpreferably 1 mm. In another example, the perforated tubes are made ofaluminum or plastic. The perforated tubes will be used to transfer gasinto the non-zero-slump concrete 216. The perforated tubes can be placedin the mould before casting concrete or inserted through the big-sizeholes after casting concrete.

The freshly prepared non-zero-slump concrete 216 is transferred into aprepared mould with any known methods in the prior arts. The mould onceagain should be air-tight and sealed using a lid designed to cover toenclose the top of the mould in one of the possible mould materials orin airtight fabrics. This lid is attached to the body of the mould withhinges, clamps and/or bolts.

The mould is once again pre-lubricated prior to casting in order tofacilitate the demoulding process 230. The wet-cast concrete or theslag-based intermediate 226 is consolidated within the mould by internalor external vibrators for no more than 120 seconds. The wet-castconcrete or the slag-based intermediate 126 does not need to be pressedor compacted inside the mould. That is, the present method in apreferred embodiment is free of being pressed or compacted. The watercontent of a slag-based intermediate 226 is to be reduced.

(iv) Pre-Conditioning 240

The process step of pre-conditioning 240 once again reduces the watercontent to that of the slag-based intermediate 226. Pre-conditioning maybe conducted in at least one of two ways. In the first method, an airflow 241 is introduced through the plurality of openings in the mouldwall (FIG. 5). In another example, air flow can be pressurized air. Thispreconditioning step reduces the initial water-to-binder content as inmethod 101. In another embodiment heating element/wires 243 are used.These wires are placed on the outside of the mould before casting thewet-cast slag-based concrete 226 (FIG. 5) or may be embedded within theslag-based intermediate 226. The wires may be placed on a steel frameacross the height of the mould at an interval of 300 mm. The heatingelements/wires may also be floor heating mats or drum heaters installedto cover the exterior surfaces of the mould. The elements heat up themould walls and eventually increase the evaporation process to reducethe moisture content of the slag-based intermediate 226. The twoembodiments for moisture reduction may furthermore be combined to useboth air 241 drying and heating 243 simultaneously.

The preconditioning 240 step continues with the escape of water vapour242 until the initial water-to-binder content is reduced was in step140.

The increase of porosity defined in terms of concrete volume created byeither of the above pre-conditioning methods in concrete is 70%,preferably 60%, preferably 50%, preferably 40%, preferably 30%,preferably 20%, preferably 10% or preferably 5% or preferably 1% ofconcrete volume. After either embodiment, the mould lid is closed andthe mould is inspected for airtightness, with careful attention to theopenings that allow the perforated tubes at the mould wall in the caseof the embodiment illustrated in FIG. 6.

At the end of the pre-conditioning 240 process, the remaining water inthe concrete should not fall below 5% of the initial water content bymass and a conditioned slag-based intermediate 246 is formed, having asecond water to binder ratio by weight that is less than the first waterto binder ratio of the non-zero-slump concrete 216. The mould is sealedair-tight after completion of the pre-conditioning step 240.

(v) CO₂ Activation\Curing 250

The conditioned slag-based intermediate 246 within the mould iscontacted with carbon dioxide, CO₂ or a gas containing CO₂. The holes onthe sides of moulds are connected to sources of gas containing CO₂ viapipes. The carbon dioxide 251 gas is introduced to cure the conditionedslag-based intermediate 146 the CO₂ is at 5%, preferably 10%, preferably20%, preferably 30%, preferably 40%, preferably 50%, preferably 60%,preferably 70%, preferably 80%, preferably 90%, or preferably 99.5%purity- and is injected into the conditioned slag-based intermediate 246at ambient temperature through the side wall openings in the mould. Thegauge pressure of the gas will gradually increase to a range of 0.1 psiand optionally to 100 psi. Although not illustrated it is understoodthat some gases may escape the mould in the CO₂ activation\curing step.

With this embodiment of the invention, the sealed mould also operates asa curing chamber. The mould is kept pressurized with carbon dioxide forno less than 10 minutes, though the CO₂ curing process can continue forup to 48 hours. The inner mould temperature will increase by at least 1°C. as a result of an exothermic, accelerated curing reaction—the “CO₂activation process”. At the end of the activation process, the remainingCO₂, if any, is vented out and the lid opened.

(vi) Demoulding 230

Demoulding occurs soon or immediately after completion of the CO₂activation process. The perforated tubes can be left inside the concreteor removed from it. Any excess lengths of tubes from the mould sidewalls, if any, are cut off and space is filled with a cement grout 255,a steel fiber reinforced cement mortar, a cement paste, a polymerconcrete or combinations thereof. The cement or polymer-based fillingmaterials within the tubes are cured for no less than 1 hour.

Upon demoulding 230 a wet-cast slag-based concrete 256 is produced.

C) An Open Mould with Gas Supplied in Curing Chamber or Enclosure

Referring to FIG. 7, a method 301 of producing a wet-cast slag-basedconcrete product 356 is illustrated that includes the steps of: casting,preconditioning and CO₂ curing in an open mould with a plurality ofholes in the mould placed in a curing chamber or other enclosure. Theenclosure may be any one of at least a chamber, an enclosed space, avessel and a room.

(i) Wet-Cast Slag-Based Concrete 356 Production.

The method 301 of producing a wet-cast slag-based concrete 356 begins aswith methods 101 and 201 by providing a composition of a non-zero-slumpconcrete 316 and uniformly mixing 310 all ingredients of a compositionthat include but are not limited to: a slag 311 and an optional at leastone other binder 313 (providing a slag-based binder 314), an aggregate315, chemical admixtures 317, fibers 319 and water 305. Thewater-to-binder ratio of the wet-cast slag-based concrete 356 used inthis innovation should be higher than the water content of dry-cast orzero-slump concrete. In a preferred embodiment the mixed non-zero-slumpconcrete 316 has a first water to binder ratio by weight of greater than0.2, preferably 0.25, preferably 0.3, preferably 0.35, preferably 0.4,preferably 0.45, preferably 0.5, preferably 0.55, preferably 0.6 orpreferably 0.65. The terms “water to slag-based binder ratio by weight”and “water to binder ratio by weight” are equivalents.

The non-zero-slump concrete 316 will preferably have a slump range of 5to 250 mm. The non-zero-slump concrete 316 is preferably workable for atleast 5 minutes. The mixing 310 should ensure that the non-zero-slumpconcrete 316 is free of signs of segregation or bleeding. The compactionfactor test for the non-zero-slump concrete 316 in a preferredembodiment is in a range of 0.7 to 1.0. The temperature ofnon-zero-slump concrete 316 before casting is preferably 0° C. to 30° C.The fresh non-zero-slump concrete 316 in a preferred embodiment has anair void content of measured by any conventional method (an exemplarystandardized test is ASTM C231 for Air Content of Freshly Mixed Concreteby the Pressure Method) should not exceed 15% of the volume of concrete.The compaction factor test is described in BS 1881-103:1993 and BS EN12350-4:2009 (BS EN 12350-4:2009, Testing fresh concrete Part 4: Degreeof compatibility). The non-zero-slump concrete 316 appropriately mixedis now ready for transfer to casting 320.

(ii) Reinforcement

In a preferred embodiment before casting the non-zero-slump concrete 316the mould is prepared and reinforcing material such as, carbon steel,stainless steel and/or FRP reinforcement bars are placed inside themould, if required. The diameter of the bars may vary from 5 mm to 60 mmwith yield strength in the range of 100 MPa to 2100 MPa. Thereinforcements to be designed in accordance with codes and standards.

(iii) Casting 320, Placement

The side walls of the mould include a plurality of openings. The mouldfor this embodiment of method 301, interestingly, neither airtight norhas a lid. The mould is made of steel, iron, aluminum, plastic, or FRP.The existing concrete moulds can also be adjusted by making holes intheir walls. The plurality of openings preferably have a diameter offrom 1 to 500 mm, or openings may have any shape with a surface area ofat least 1 mm². The openings in the mould side walls allow air (andsubsequently CO₂) to enter the mould while the mould is within a curingchamber or other enclosure. The space between each of the openings inany direction is preferably less than 1000 mm as shown in FIG. 8.Optionally the openings can be filled temporarily with stoppers toprevent fresh non-zero-slump concrete 316 from leaking out of the mouldupon transfer of non-zero-slump concrete 316; rubber stoppers are acommon option. If stoppers are used, they should be removed prior toallow the passage of gases for the pre-conditioning and carbonationcuring steps 340 and 350 respectively.

The freshly prepared non-zero-slump concrete 316 is transferred byappropriate means and cast in a prepared mould with any known methods inthe prior arts.

The mould should be pre-lubricated prior to casting in order tofacilitate the demoulding process 330. The wet-cast concrete or theslag-based intermediate 326 is consolidated within the mould by internalor external vibrators for no more than 120 seconds. The wet-castconcrete or the slag-based intermediate 126 does not need to be pressedor compacted inside the mould. That is, the present method in apreferred embodiment is free of being pressed or compacted. The watercontent of a slag-based intermediate 326 must be reduced.

(iv) Pre-Conditioning 340

The process step of pre-conditioning 340 reduces the water content 342of (the slag-based intermediate 326 now). Pre-conditioning may beconducted in at least one of two ways. In the first method, air flow orpressurized air 341 is introduced into inside or outside of the curingchamber or enclosure. The method in a further embodiment uses heatingelements/wires 343. These wires are placed on or near the mould wallsbefore casting 320 the concrete (FIG. 7). They are optionally placed ona steel frame across the height of the mould at an interval of 300 mm.The heating wires and frame are left inside the concrete when it is castand after concrete is cured. An electric current can then be passedthrough the frame and wires. The heating elements/wires may also befloor heating mats or drum heaters installed so as to cover the exteriorsurfaces of the mould. The elements heat up the mould walls andeventually increase the evaporation process to reduce the moisturecontent of the concrete. The two methods may furthermore be combined toinclude both air 341 drying and heating 343.

The preconditioning 340 step continues until initial water-to-bindercontent is reduced by up to 90%, preferably 80%, preferably 70%,preferably 60%, preferably 50%, preferably 40%, preferably 30%,preferably 20% and preferably 10% or preferably 2%.

The increase of porosity defined in terms of concrete volume created byeither of the above pre-conditioning methods in concrete is 70%,preferably 60%, preferably 50%, preferably 40%, preferably 30%,preferably 20%, preferably 10% or preferably 5% or preferably 1% ofconcrete volume. After either method, attention/inspection of theplurality openings ensures that air will contact the slag-basedintermediate 326.

At the end of the pre-conditioning 340 process, the remaining water inthe concrete should not fall below 5% of the initial water content bymass and a conditioned slag-based intermediate 346 is formed, having asecond water to binder ratio by weight that is less than the first waterto binder ratio of the non-zero-slump concrete 316.

(v) CO₂ Activation\Curing 350

The conditioned slag-based intermediate 346 is contacted with carbondioxide, CO₂ or a CO₂ containing gas from the curing chamber or suitablegas enclosure. The carbon dioxide 351 gas is introduced to cure theconditioned slag-based intermediate 346 at 5%, preferably 10%,preferably 20%, preferably 30%, preferably 40%, preferably 50%,preferably 60%, preferably 70%, preferably 80%, preferably 90%, orpreferably 99.5% purity—into the conditioned slag-based intermediate 346at ambient temperature from the atmosphere of the curing chamber orenclosure through the plurality of openings in the side wall of themould. The gauge pressure of the chamber/enclosed space/vessel/room willgradually increase to a range of 0.1 psi to 100 psi. Although notillustrated it is understood that some gases may escape the chamber orenclosure during the CO₂ activation\curing step.

With this embodiment of the invention, mould is kept pressurized withcarbon dioxide for no less than 10 minutes, though the CO₂ curingprocess can continue for up to 48 hours. The inner mould temperaturewill increase by at least 1 C as a result of an exothermic, acceleratedcuring reaction—the “CO₂ activation process”. At the end of theactivation process, the remaining CO₂, if any, is vented out of thecuring chamber or enclosure.

FIG. 8 illustrates the casting 320, pre-conditioning 340 and the CO₂curing 350 steps in a front view section of an un-sealed mould accordingto one embodiment method 301 described herein in FIG. 7

(vi) Demoulding 330

Demoulding occurs soon or immediately after the CO₂ activation process.

Upon demoulding 330 a wet-cast slag-based concrete 356 is produced.

Some parameters for production of 1 cubic meter of concrete by themethods described herein:

Steel slag content=600 kg, A first water/binder ratio=0.35; Slump=5 mm,Preconditioning method=air flow

Steel slag content=500 kg; Limestone powder=50 kg, A first water/binderratio=0.55; Slump=200 mm, Preconditioning method=air flow

Stainless slag content=350 kg; A first water/binder ratio=0.45; Polymerpowder=50 kg, Hydraulic cement=30 kg; Fly ash=200 kg, Slump=100 mm,Preconditioning method=pressurized air

Steel slag content=400 kg; Non-hydraulic cement=100 kg; A firstwater/binder ratio=0.4; Preconditioning method=heaters

Stainless slag content=480 kg; A first water/binder ratio=0.45; silicafume=20 kg, Corrosion inhibitor=5 kg, Preconditioning method=heatingelement wires

Steel slag content=650 kg; A first water/binder ratio=0.45; Airentraining admixture=2 litre, Slump=120 mm; Preconditioningmethod=heating element wires

Steel slag content=700 kg; A first water/binder ratio=0.45; Steelfiber=80 kg, Viscosity modifying admixture=1 litre, Slump=50 mm;Preconditioning method=air flow

Steel slag content=1200 kg, A first water/binder ratio=0.30;Superplasticizer=15 litre, Water repellent=5 litre, Slump=150 mm;Preconditioning method=pressurized air

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing form the inventions disclosed. Still othermodifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure and such modifications are intended to fall within theappended claims.

The invention claimed is:
 1. A method of producing a wet-cast slag-basedconcrete product comprising steps of: 1) providing a slag-based binder,an aggregate and water; 2) mixing the slag based binder, the aggregateand the water to produce a workable non-zero-slump concrete compositioncomprising a first water to slag-based binder ratio by weight of greaterthan 0.2; 3) a) casting and/or placing the non-zero-slump concrete bytransferring and/or consolidating the non-zero-slump concretecomposition into an air-tight mould wherein said air-tight mould iscomprising at least one gas pipe and/or at least one gas lance; or b)casting and/or placing the non-zero-slump concrete by transferringand/or consolidating the non-zero-slump concrete composition into anair-tight mould and further comprising a step of inserting the at leastone gas pipe and/or the at least one gas lance into the non-zero-slumpconcrete composition; or c) casting and/or placing the non-zero-slumpconcrete by transferring and/or consolidating the non-zero-slumpconcrete composition into an air-tight mould, the mould comprising amould wall and a plurality of inlets in the mould wall, wherein theplurality of inlets are optionally closed to retain the non-zero-slumpconcrete; or d) casting and/or placing the non-zero-slump concrete bytransferring and/or consolidating the non-zero-slump concretecomposition into a mould, the mould comprising a mould wall defining anopen top surface and a plurality of inlets in the mould wall, whereinthe plurality of inlets are optionally closed to retain the workablenon-zero-slump concrete; 4) pre-conditioning the non-zero-slump concretecomposition within the mould with at least one of i) air flow and/orpressurized air from the at least one gas lance, if one of options 3a)or 3b) is selected, ii) heaters and iii) heating element wires embeddedin the non-zero-slump concrete, to produce a pre-conditioned slag-basedintermediate comprising a second water to slag-based binder ratio byweight that is less than the first water to slag-based binder ratio byweight; 5) sealing the air-tight mould when the casting corresponds tocasting step 3a), 3b) or 3c); 6) after steps 2) to 5), curing thepre-conditioned slag-based intermediate with a gas containing carbondioxide; from the at least one gas pipe and/or the at least one gaslance when the casting and/or placing the non-zero-slump concrete bytransferring and/or consolidating the non-zero-slump concretecomposition corresponds to step 3a) or 3b); or via the plurality ofinlets in the mould wall when the casting and/or placing thenon-zero-slump concrete by transferring and/or consolidating thenon-zero-slump concrete composition corresponds to step 3c); or in achamber/enclosed space/vessel/room via the plurality of inlets in themould wall and the open top surface when the casting and/or placing thenon-zero-slump concrete by transferring and/or consolidating thenon-zero-slump concrete composition corresponds to step 3d), to producea moulded wet-cast slag-based concrete product, and 7) after the curingof the pre-conditioned slag-based intermediate, demoulding the mouldedwet-cast slag-based concrete product to provide the wet-cast slag-basedconcrete product.
 2. The method of claim 1, wherein the step of castingof the non-zero-slump concrete is free of pressing/compaction.
 3. Themethod of claim 1, further comprising a step of filling a hollow spacewithin the at least one gas pipe and/or lance with cement grout, steelfiber reinforced cement mortar and/or cement paste, after said step ofcuring.
 4. The method of claim 1, wherein the gas pipe and/or lance isinserted after casting the non-zero-slump concrete composition.
 5. Themethod of claim 1, wherein the slag-based binder is a slag—free of ormixed with at least one other binder selected from the group consistingof fly ash, calcinated shale, silica fume, zeolite, GGBF (GroundGranulated Blast Furnace) slag, limestone powder, hydraulic cements andnon-hydraulic cements.
 6. The method of claim 5, wherein the slag isselected from the group consisting of a steel slag, a stainless steelslag, a basic oxygen converter sludge, blast furnace sludge, aby-product of zinc, iron, copper production and combinations thereof. 7.The method of claim 1, further comprising a reinforcing step of placinga reinforcing material into the air-tight mould before the casting ofstep 3).
 8. The method of claim 7, wherein the reinforcing material iscarbon steel, stainless steel and/or FRP reinforcement bars.
 9. Themethod of claim 1, wherein a cumulative calcium silicate content of theslag is at least 20 weight %.
 10. The method of claim 1, wherein thestep of pre-conditioning is conducted to provide an increased porosityof at least 1% of volume of the wet-cast slag-based concrete.
 11. Themethod of claim 1, wherein the non-zero-slump concrete composition has aslump value in a range of 5 mm to 250 mm.
 12. The method of claim 1,wherein the non-zero-slump concrete composition has a compaction factortest for fresh concrete ranging from 0.7 to 1.0.
 13. The method of claim1, wherein the slag-based binder is steel slag selected from the groupconsisting of reducing steel slag, oxidizing steel slag, converter steelslag, electrical arc furnace (EAF) slag, basic oxygen furnace (BOF)slag, ladle slag, fast-cooled steel slag and slow-cooled steel slag andcombinations thereof.
 14. The method of claim 1, wherein the wet-castslag-based concrete product is selected from the group consisting ofprecast, reinforced and non-reinforced concrete pipes, box culverts,drainage products, paving slabs, floor slabs, traffic barriers, walls,manholes, retaining wall, pavers, tiles, and shingles.
 15. The method ofclaim 1, wherein the wet-cast slag-based concrete comprises of a slagcontent of at least 5% by weight.
 16. The method of claim 1, wherein thenon-zero-slump concrete composition further comprises at least one ofaccelerator, retarder, viscosity modifying agent, air entertainer,foaming agent, ASR (alkali silica reaction) inhibitor, anti-wash-out,corrosion inhibitor, shrinkage reducer, concrete crack reducer,plasticizer, super plasticizer, sealer, paint, coating, water reducer,water repellant, efflorescence control, polymer powder, polymer latexand workability retainer.
 17. The method of claim 1, wherein thenon-zero-slump concrete composition further comprises at least one ofcellulose fiber, glass fiber, micro synthetic fiber, natural fiber, PPfiber, PVA fiber and steel fiber.
 18. The method of claim 1, wherein thecuring of the pre-conditioned slag-based intermediate with the gascontaining carbon dioxide is free of additional external sources of heatand/or energy.
 19. The method of claim 1, wherein the gas containingcarbon dioxide is a gas containing a concentration of CO₂ of at least 5%by volume.
 20. The method of claim 1, wherein, in step 6c), a perforatedtube is inserted through at least one of the plurality of inlets in saidmould wall.
 21. The method of claim 20, wherein the perforated tube isinserted into the air-tight mould interior and traverses either fully orpartially to an opposite mould wall.